Interference rejection receiver



Feb 20, 1940. D. v. slNNlNGER INTERFERENGE REJECTION REc'IvEB Filed April 26, 1939 IIIIL 55 arrangement, however, differs in impcrtant reter-poise s. The phase of these potentials with 5g Patented Feb. 20, 1940 l o I u UNITED STATES PATENT OFFICE.

n l2,190,850 Imonummer. nemer-10N asoman Dwight v. sinnmg'er, chicago, n1., signor to Johnson Laboratories, Inc., Chicago, .111., `a corporation of Illinois Application April 26, 1939, Serial N0. 270,194

` 6 Claims. (Cl. Z50-20) This invention relates to high-frequency cirspects from that of my invention, as will become cuits and more particularly to those employed'in apparent from my specincation. radio receiving systems. Such systems include My invention is particularly adapted for use means for collecting the high-frequency signals in connection with resonant circuits which are which are radiated from relatively distant transtuned over a range of frequencies by inductance 5 mitting stations. Such a collecting means is of variation. Such al system is the one disclosed by the capacitive or inductive type. The improved Polydoroif in United States Patent No. 1,940,228, collecting means incorporated in the present in in which a resonant circuit having an inductance vention is of the inductive type. y coil and capacitor is adjusted over a range of 10 In radio receivers, and more particularly those frequencies by movement of a compressed com- 10 intended for the reception of broadcasting, it is minuted ferromagnetic core relative to the invery important that the signal-to-noise ratio at ductance coil. This method of tuning is comthe input to the rstvacuum tube be as high as monly called permeability tuning. An improved possible. This ratio may be increased either by form of such a system is disclosed by Schaper increasing the amount of signal pick-up or by in United States Patent No. 2,051,012. Both l5 decreasing the noise pick-up, or by both simul- Polydoroffs original system and Schapers imtaneously. The signal pick-up may be improved proved system readily cover an adequate range by increasing the physical dimensions of the sigof frequencies and may easily-be ganged to pronal-collecting means or by tuning the circuit vide-multiple unit systems. It will be underincluding the signal-collecting means to reson'- stood, however, that my invention is equally 20 ance with the desired signal or both. The noise useful in capacitively tuned systems. pick-up may be reduced by preventing the signal- An object of my invention is to provide an collecting means from'picking up 'certain forms improved signal-collecting means for radio reof interference or by supplying to the input circeivers.

cuit of the nrst vacuum tube of the receiver a l An additional object is to improve the signal- 25 voltage equal in amplitude but opposite in phase to-noise ratio which. may be obtained with a to the noise which is picked .up by the signalcompact signal-collecting means.

collecting means. Still another object is to provide a tuned input In accordance with my invention,' I- employ circuit for radio receivers which is capable of an electro-statically shielded loop antenna as a providing an improved signal-to-noise ratio. 30

signal-collecting means and arrange to tune the These and other objects are realized in accordcircuit in which it is connected to resonance with ance with my invention in a manner which will the desired signal. Additionally, I provide means be more readily understood by reference to the for introducing into the input circuit of the first accompanying drawing, in which: vacuum tube a voltage which tends to overcome Fig. 1 shows schematically an input system ,35

the voltage there present due to noise pick-up embodying my invention; by the signal-collecting means. My invention Fig. 2 shows a preferred arrangement accordprovides, therefore, in compact and inexpensive ing to the invention; and form, a system having a signal-to-noise ratio Figs. 3 and 4 show modifications of the arcomparable with that formerly obtainable only rangement of Fig. 2, i 40 by the use 0f a relatively` Ierse capacitive an- In the input system cf Fig. 1, which is suitable tenne, 0r by the use 0f a bulky loop antenna of for use in radio receivers or the like, the resonant the type which must bewtated for satisfactory circuit which is designated generally by the refresults with various Signals originating in seoerence numeral I includes a signal-collecting graphically different locations. loop 2, an inductor 3, and a capacitor li. Loop 45 Inan article entitled A shielded loop for noise 2 is housed in a conductive shield or sheathing 5 IedllCtOIl in bl'OadOaSt reception appearing at the electrical center of which is grounded at G Page 20 0f the October 1938 issue of Elecand the ends of which are respectively connected tronics magazine, Goldman describes the use to the end terminals of a potentiometer l. The of a pivotally mounted eleotrostatically shielded movable arm or slider 8 of the potentiometer is 50 loop antenna which is tuned to resonance with connected to counterpoise 9. Loop 2, sheathing the desired signal by capacitance variation, noise 5, potentiometer 1 and counterpoise 9 in comreduction being realized by properly orienting bination constitute means for introducing into the loop with respect to the noisesource. This resonant circuit l potentials picked up by counrespect to that of the noise potentials in circuit I is determined by the direction in which slider 8 is moved, and their amplitude by the amount of such movement. l

Thus it will be seen that my improved input system comprises Va resonant circuit I including a loop 2, an inductor 3, and a capacitor 4,l and the system is connected to supply voltage through capacitor I to control-grid II ofvacuum tube I2, direct-current bias voltage being supplied to control-grid I I'from any suitable source through resistor I3.

It will be understood that loop 2,-, although shown diagrammatically as a single turn, lactually consists of several turns. Loop 2 will ordinarily be mounted in such a way as to permit it to be rotated about a vertical axis, since by this means maximum signal pick-up is secured, but this is not an essential requirement vfor the successful operation yof my invention. Counterpoise 9, shown by the conventional symbol, may in practice have any one of a number of different forms, as for example a few feet of wire attached to the cabinet housing the receiver employing the invention.` Vacuum tube I2 is the first tube of a radio receiver or the like, and may function either as an amplifier or otherwise, for example as the first detector of a superheterodyne radio receiver, without affecting the mode of operation of the invention..

In operation, resonant circuit I is tuned to resonance with the desired signal. The two halves of loop sheathing with potentiometer 'I comprise a bridge circuit by means of which the amplitude and phase of the voltage which is supplied to resonant circuit I from counterpoise!!- may be varied as desired. Thus electrostatically introduced interference may be bucked out by the introduction of a voltage of equal amplitude but of opposite phase. This is done merely by adjustment of potentiometer 'I to the null point. By means of this adjustment, it is also possible to' substantially offset electromagnetically introduced interference arising'with random orientations of the loop. In this manner, a very substantial reduction of noise is realized Without the necessity for changing the orientation of loop 2. This is an important feature of my invention and greatly simplifies the construction and operation of the receiver utilizingmy system. Thus, in accordance with my invention, I realize mostof the advantages of the loop type of antenna Without the requirement of rotating it for minimum noise. The system described by Goldman, mentioned above. is incapable of providing this highly desirable result. Still Vfurther noise reduction may be obtained, however, byrotating loop 2 to the bearing providing the least pick-up from the.

interference SOul'Ce.

Another feature of my invention is that, in quiet locations, the signal pick-up of counterpoise 9 may be made to supplement that of loop -2 merely by moving slider 8 of potentiometer 1 to either extremity. Where maximum sensitivity is required, an ordinary antenna may be connected to counterpoise 9 or in place of it, thus rendering the` receiver incorporating my invention suitable for use in so-called dead spots or other locations of relatively poor signal strength, and in any locations for the reception of very Weak signals.

Referring now to Fig. 2, which shows a preferred embodiment of the invention and in which like reference numerals are used to designate like components, it-will be seen that the inductor 3 of Fig. 1 is replaced by a variable inductance device I4 comprising an inductance coil I5 and a relatively movable ferromagnetic core I6. Inductance device I4 is used for tuning resonant circuit I over a range of frequencies, and capacitor 4, which is adjustable, may be employed for adjusting the resonant frequency near the highfrequency end of the tuning range. Core I6 has appreciable surface conductivity and is effectively grounded, either conductively orA through a lowimpedance resistive or capacitive path. The capacitance between the core I6 and the high-potential portion of coil I5 is represented by dotted capacitor I'I`, and this capacitance varies as core I6 moves relatively tofcoil I5, as indicated by the curved arrow passing through it. 'Ihe arrangement and mode of operation of the embodiment shown in Fig. 2 is otherwise similar to that of the system of Fig. 1. A In Figs. 1 and 2,` sheathing 5 serves simultaneously as an electrostatic shield for loop 2 and as a primary winding for applying signals originatmg 1n counterpoise 9 to resonant circuit I.

' This is a preferable arrangement and one of the features of my invention, but it is within the scope of the invention to employ a separate primary winding' This modification is shown in Fig. 3, in which like components are designated by like reference numerals.A Potentiometer I, instead of being connected to the ends of sheathing 5, as in Figs.'1 and 2, is connected betweenthe ends of a primary winding I8 which is inductively coupled to loop 2 and the approximate electrical center of which is grounded. In other respects, the arrangement and operation of the modification of Fig. 3 is the same as in he case of the systems of Figs. 1 and 2.

Where the interference encountered is of the resonant type, i. e., such as to undergo an increase in a resonant circuit, good results may be obtained by employing a loop which is not shielded electrostatically. Fig. 4 lshows such a modification in which like reference numerals are used to desig- .nate like components. In contrast with Figs. 1, 2

and 3, loop 2 of Fig. jl/ is unshielded and potentiometer 1 is connected between its ends.' The low-potential terminal of capacitor 4 is not grounded, resonant circuit I being grounded by means of the connection I9 near the electrical center of loop 2. Although effective in overcoming resonant interference, the system of Fig. 4 is inferior to those of Figs. 1, 2 and 3 in cancelling non-resonant interference.

In Figs. 2, 3 and 4, tuning of resonant circuit I over a range of frequencies is accomplished by movement of core I6 with respect to coil I 5. With the core withdrawn,'the resonant frequency is adjusted to the desired value by means of capacitor 4. Core I6 may -be ganged with other cores in the receiver for single-control operation if desired. Since the proportion of loop inductance to total inductance in resonant circuit IA employed in the systems of Figs. 2, 3 and 4 without departing from the scope of my invention. In Figs. 2 and 3, the use of inductance tuning prevents the inherent capacitance between loop 2 and sheathing from curtailing the frequency range overwhich resonant circuit I is tunable.

In one successful embodiment in accordance with Fig. 2, loop 2 consists of iive turns of No. 22 insulated wire enclosed in shield 5 consisting of a split copper tube with an inside diameter of 0.3125 inch and an outside diameter of 0.375 inch. Loop 2 is 12.5 inches in diameter, and is preferably mounted so as to rotate freely about a vertical axis. Potentiometer 'I has a resistance of 5000 ohms. Counterpoise 9 consists of about ten feet of insulated wire. Inductance coil I5 comprises 277 turns of No. 36 enamelled wire forming a winding 1.6875 inches longon a form having an outside diameter of 0.340 inch, and the coil has an lnductance of approximately 125 microhenries. Core I6 has a length of 1.875 inches and a diameter of 0.3125 inch. Capacitors l and I0 have capacitances of 37 and 500 micromicrofarads, respectively. Resistor I3 has a resistance of 0.5 megohm. This embodiment is intended for use over the frequency range from 540 to 1600 kilo-` cycles.

Although suitablefor use in any type of radio receiver, my invention is particularly applicable in portable battery-operated receivers of the socalled suitcase type, where the maximum signal pick-up consistent rwith extreme compactness is essential and where it may or may not be convenient to orient the self-contained loop for minimum interference.' Other uses will readily occur to those skilled in the art.

Having thus described my invention, what I claim is:

' 1. An input system for use in radio receivers and the like, comprising a resonant circuit including a signal-collecting loop, a counterpoise,

and means for introducing into said circuit potentials of opposite phase but otherwise substantially identical to noise potentials occurring in said circuit comprising a potentiometer coupled to said loop and having its movable arm connected to said counterpoise, whereby said noise potentials may be effectively cancelled with resultant improvement in the signal-to-noise ratio of said circuit. t

2. An input system for use in radio receivers and the like, comprising a resonant circuit including a signal-collecting loopI having a conductive sheathing grounded at approximately its electrical center, a counterpoise, and means for inducing 'into said circuit potentials of ,opposite phase but otherwise substantially identical to noise potentials occurring in said circuit comprising a potentiometer having its end terminals connected respectively to the ends of saidsheathing and having its movable arm connected to said counterpoise, whereby said noise potentials may be eiectively cancelled with resultant improvement in the signal-to-noiseratio of said circuit. l

3. An input system for use in radio receivers and the like. comprising a resonant circuit including an electrostatically shielded signal-00L p lecting loop; a counterpoise; and means for inducing into said circuitpotentials of opposite phase but otherwise substantially identical to noise potentials occurring in said circuit comprising a. Winding inductively coupled to said loop and being grounded at approximately its electrical center, and a potentiometer having its end terminals connected respectively to the ends of said winding and having its movable arm connected to said counterpoise; whereby said noise potentials may be effectively' cancelled with resultant improvement in the signal-to-noise ratio of said circuit.

4. An input system for use in radio receivers and the like, comprising a resonant circuit including an unshielded signal-collecting loop having its approximate electrical lcenter grounded, a counterpoise, and means for introducing into said circuit potentials of opposite phase but otherwise substantially identical to noise potentials occurring in said circuit comprising a potentiometer having its end terminals connected respectively to` the ends of said loop and having its movable arm connected toV said.l counterpoise, whereby said noise potentials may be eectively cancelled with resultant improvement in the signal-to-noise ratio of said circuit.

5. An input system for use in radio receivers and the like, comprising a resonant circuit including a signal-collecting loop, a variable inductance device for tuning said circuit over a range of frequencies comprising an inductance coil and a relatively movable ferromagnetic core oi.' appreciable surface conductivity and eiective- 1y grounded, and an adjustable capacitor for adjusting the resonant frequency of said circuit near the high-frequency end of said range; and

means for introducing into said circuit potentials of opposite phase but otherwise substantially identical to noise potentials occurring in said circuit; whereby the capacitance between said ycore and said inductance coil tends to maintain 6. An input system for use in radio receiversv noise potentials occurring in said circuit cornprising a potentiometer having its end terminals connected respectively to the ends of said sheathing and having its movable arm connected to said counterpoise; whereby said noise potentials may be eiectively cancelled with resultant improvement in the signal-to-noise ratio of said circuit.

DWIGHT V. 'SINNINGER 

